The invention described herein relates to coordinate measurement machines and particularly to an arrangement for applying a constant load on the machine measuring probe to help assure accurate measurements.
Coordinate measurement machines are primarily used to mechanize the inspection of parts and components which are machined or otherwise manufactured to relatively small tolerances. Commercially available machines conventionally used for carrying out inspection processes, include a heavy base casting which supports a surface plate and structural components designed to permit movement of a high precision carriage. The carriage contains a sensitive probe which measures the coordinate dimensions of machined parts, sizes and locations of holes, and the like, on either X--Y axes or X--Y--Z axes. To obtain such movements, high precision ball or needle bearing, cylindrical sleeves, rack and pinion gears, or a combination of these are used to obtain probe measurements with great accuracy. As the probe is moved into contact with a component to be measured, an electric signal is generated corresponding to the coordinates measured which is then digitally displayed on an electronic console.
Although the coordinate measurement system is designed to provide freedom of carriage movement with minimum hand pressure when the probe contacts the component being measured, it has been found that when highly precise measurements are required, i.e., to within .0001 inch operator hand pressure plays an important part in the accuracy of measurements. Either too much or too little hand pressure against the probe may often provide coordinate dimensions or measurements which are beyond the tolerances permitted for the particular part being measured. This occasionally results in scrapping or reworking of the part when the need actually did not exist. Before undertaking such reworking or scrapping of the part, the measuring process must be repeated using greater care to confirm or deny such original readings. Such actions involving reworking of parts or repetition of the measuring process results not only in high cost manufacturing operations, but also cause delays in component parts shipments which disrupts schedules of both the part manufacturer and those to whom such parts are shipped.